For Aristotle, the exercise of certain behaviors in natural bodies is teleological. It is for the sake of an end. The process in which human beings acquire reason in is an example. Human beings acquire reason for the sake of becoming like the unmovable first mover. The presence of reason makes the human existence like the divine existence.
The Cosmos has a Maker
In the Timaeus, a divine maker (the "demiurge" (δημιουργὸς)) who is good arranges things so that everything in the cosmos is as like himself as possible.
"[E]verything which becomes must of necessity become owing to some cause (αἰτίου).... [W]hen the artificer (δημιουργὸς) of any object, in forming its shape and quality, keeps his gaze fixed on that which is uniform, using a model of this kind, that object, executed in this way, must of necessity be beautiful (καλὸν); but whenever he gazes at that which has come into existence and uses a created model, the object thus executed is not beautiful. Now the whole heaven (πᾶς οὐρανὸς), or cosmos (κόσμος), or if there is any other name which it specially prefers, by that let us call it,—so, be its name what it may, we must first investigate concerning it that primary question which has to be investigated at the outset in every case,—namely, whether it has existed always, having no beginning of generation, or whether it has come into existence, having begun from some beginning. It has come into existence; for it is visible and tangible and possessed of a body; and all such things are sensible, and things sensible, being apprehensible by opinion with the aid of sensation, come into existence, as we saw, and are generated. And that which has come into existence must necessarily, as we say, have come into existence by reason of some cause. Now to discover the maker and father (ποιητὴν καὶ πατέρα) of this universe were a task indeed; and having discovered him, to declare him unto all men were a thing impossible. However, let us return and inquire further concerning the cosmos,—after which of the models did its architect construct it? ... [I]t is clear to everyone that his gaze was on the eternal; for the cosmos is the fairest (κάλλιστος) of all that has come into existence, and he the best (ἄριστος) of all the causes" (Timaeus 28a). He was good (ἀγαθὸς), and in him that is good no envy ariseth ever concerning anything; and being devoid of envy he desired that all should be, so far as possible, like unto himself (πάντα ὅτι μάλιστα ἐβουλήθη γενέσθαι παραπλήσια ἑαυτῷ). This, then, we shall be wholly right in accepting from men of wisdom as being above all the supreme originating principle (ἀρχὴν) of becoming and the cosmos" (Timaeus 29d).
Why human beings have eyesight
The divine maker ensures that human beings have the sense of sight so that through exercise of this ability they can make themselves better by making their minds more orderly. Seeing is part of a process that gives rise to the love of wisdom and that ultimately transforms human beings so that their thinking "imitat[es] the completely unstraying revolutions of the god"
"Let us conclude our discussion of the auxiliary causes that gave our eyes the power they now possess. We must next speak of that supremely beneficial function for which the god gave them to us. As my account has it, our sight has proved to be a source of supreme benefit to us, in that none of our present statements about the universe could ever have been made if we had never seen any stars, sun or heaven. The ability to see the periods of day-and-night, of months and of years, of equinoxes and solstices, has led to the invention of number, and has given us the idea of time and opened the path to inquiry into the nature of the universe. These pursuits have given us the love of wisdom (φιλοσοφίας), a gift from the god to the mortal race whose value neither has been nor ever will be surpassed. This is the supreme good our eyesight offers us. ... The god invented sight and gave it to us so that we might observe the orbits of intelligence in the universe and apply them to the revolutions of our own understanding. For there is a kinship between them, even though our revolutions are disturbed, whereas the universal orbits are undisturbed. So once we have come to know them and to share their ability to make correct calculations according to nature, we should stabilize the straying revolutions within ourselves by imitating the completely unstraying revolutions of the god" (Timaeus 46e-47c).
The Unmovable First Mover
Aristotle argues that there can be no first or last moment of time, that time is an attribute of change, and that the cause of this everlasting change must be free from change. This conception of the universe rules outs a teleological explanation of things in terms of divine maker understood on the model of an "artificer" (δημιουργὸς), but Aristotle does not think that it makes teleological explanation itself impossible. He thinks that "the first unmovable mover" (τὸ πρῶτον κινοῦν ἀκίνητον) is the starting-point for a teleological explanation for why things are the way they are.
The motion of the stars is circular
The unmovable first mover is the teleological cause the the fixed stars moving eternally in a circle. It causes this change without itself changing. Just what Aristotle thought happens is not very clear, but his idea seems to be that eternally moving in a circle is a behavior that belongs to the stars because this is the way their existence is like the existence of the unmovable first mover.
(Most of the objects in the night sky visible to the naked eye appear to move together in the same relative arrangement night after night. These objects are the "fixed stars." Some of the visible objects in the night sky appear to change their position relative to the fixed stars. These objects are the "wandering stars" (ἀστέρες πλανῆται). The wandering stars are the planets.)
"It is impossible that movement should come into being or cease to be; for it must always have existed. Nor can time come into being or cease to be; for there could not be a before or after if time did not exist. It follows that movement is continuous in the way time is; for time is the same thing as movement or an attribute of movement. And there is no continuous movement except movement in place, and of movement in place only that which is circular is continuous. But even if we are to suppose that there is something which is kinetic and productive although it does not actually move or produce, there will not necessarily be motion; for that which has a potentiality may not actualize it. ... And it will still not be enough even if it does function, if its essence is potentiality; for there will not be eternal motion, since that which exists potentially may not exist. There must be a starting-point (ἀρχὴν) whose substance (οὐσία) is actuality (ἐνέργεια)" (Metaphysics XII.7.1071b). "The first heaven (πρῶτος οὐρανός), then, must be eternal, and something must move it. And since that which is moved and moves is intermediate, there is a mover which moves without being moved, being eternal, substance, actuality" (Metaphysics XII.7.1072a). "Such, then, is the starting-point upon which the heaven and nature depend. Its life is like the best which we temporarily enjoy. It must be in that state always, which for us is impossible.... Actuality is thought to be the intellect (νοῦς) the divine possesses, and contemplation (θεωρία) is that which is most pleasant and best. ... If, then, the state the god (ὁ θεὸς) always enjoys is as great as that which we enjoy sometimes, it is marvelous; and if it is greater, this is still more marvelous. Nevertheless it is so. Moreover, life belongs to god. For the actuality of intellect is life, and god is that actuality; and the essential actuality of god is life most good and eternal. We hold, then, that god is a living being, eternal, most good" (Metaphysics XII.7.1072b).
Why human beings acquire reason
The unmovable first mover is also the teleological cause of behaviors common to natural bodies of a given kind in the realm below that of the stars and other heavenly bodies.
"First, then, we must speak of food and reproduction; for the nutritive soul belongs to all other living creatures besides man, and is the first and most widely shared faculty of the soul, in virtue of which they all have life. Its functions are reproduction and the assimilation of food, as a living thing that has reached its normal development and is unmutilated, and whose mode of generation is not spontaneous, naturally produces another like itself, an animal producing an animal, and a plant a plant, in order that, as far as its nature allows, it may partake in the eternal and divine (τοῦ ἀεὶ καὶ τοῦ θείου). Each strives for this and for the sake of this performs all its natural functions (πάντα γὰρ ἐκείνου ὀρέγεται, κἀκείνου ἕνεκα πράττει ὅσα πράττει κατὰ φύσιν). ... However, since they cannot share in the eternal and divine by continuity of existence, because no perishable thing can remain numerically one and the same, they share in these in the only way they can, some to a greater and some to a lesser extent; what persists is not the individual itself, but something in its image, not one in number but one in form (ἀριθμῷ μὲν οὐχ ἕν, εἴδει δ᾿ ἕν)" (One the Soul II.4.415a).
Induction too is an instance of teleological causation. Human beings naturally undergo the process of induction because this is a way human existence naturally becomes like the existence of the unmovable first mover. Acquiring reason and its knowledge is a step in the direction of the "contemplation" (θεωρία) that characterizes the existence of the unmovable first mover.